Genetic parameters for reproduction rate in the Tygerhoek Merino flock. 2. Genetic correlations with wool and live mass traits

Abstract

Data of the Tygerhoek Merino flock were used to obtain estimates of genetic correlations of 18 months wool and pre-mating live mass traits with average reproduction over two to five lambing opportunities, as well as between pre-mating live mass and subsequent reproduction in age groups of 2 - 6 years by paternal halfsib procedures. The wool traits considered were clean fleece mass (CFW), greasy fleece mass (GFW) and fibre diameter (FD). Reproduction traits were lambs born/ewe conceived (Lb!Ec), lambs born/ewe mated (Lb/Em), and lambs weaned/ewe mated (Lw/Em). The genetic correlations of 18 months wool traits with reproduction traits were not very accurate and estimates larger than twice their standard errors were obtained only on a few occasions. The genetic correlation between CFW and Lb/Ec tended to be positive. There was, however, evidence of a negative genetic correlation between CFW and the composite trait of Lw/Em both in literature cited and in the present investigation. The genetic correlations of 18 months FD with reproduction traits were variable. The genetic correlation of live mass with reproduction traits was positive, both within age groups and when 18 months pre-mating live mass was correlated with average reproduction over a number of lambing opportunities. Several estimates involving Lb/Ec, Lb/Em, and Lw/Em were larger than twice their obtained standard errors. The obtained genetic correlations were in correspondence with literature cited. It was concluded that selection for live mass is unlikely to cause negative correlated responses in reproduction, unless live mass at a very young age is used as a selection criterion.

Data van die Tygerhoek-Merinokudde isgebruik om beramings van genetiese korrelasiesvan 18-maande-wol- en liggaamsmassa-eienskappe met gemiddelde reproduksie oortwee totvyf lamgeleenthede en van paarmassa met daaropvolgende reproduksie binne ouderdomsgroepe volgens halfsibmetodes te bereken. Die woleienskappe wat ondersoek is, was skoonvagmassa (CFW), rouvagmassa en veseldikte (FD). Reproduksie-eienskappe was lammers gebore/ooi beset (Lb/Ec), lammers gebore!ooi gepaar (Lb/Em) en lammers gespeen/ooi gepaar . (Lw/Em). Die genetiese korrelasies van 18-maande-woleienskappe met reproduksiewas nie baie akkuraat nie en beramingsgroter as twee maal hul standaardfoute is slegs by 'n paar geleenthede verkry. Die genetiese korrelasie tussen CFW en Lb/Ec was oorwegend positief. Daarteenoor was daar aanduidings van 'n negatiewe genetiese korrelasie tussen CFWen die saamgestelde eienskap Lw/Em, beide in aangehaalde Iiteratuur en in die huidige ondersoek. Die genetiese korrelasie van FD met reproduksie was veranderlik. Die genetiese korrelasie van Iiggaamsmassa met reproduksie-eienskappe was positief, beide binne ooi-ouderdomsgroepe en tussen 18-maande-paarmassa en gemiddelde reproduksie cor 'n aantal lamgeleenthede. Etlike beramings op Lb/Ec, Lb/Em en Lw/Em was meer as twee maal groter as hulle verkree standaardfoute. Die beraamde genetiese korrelasies was in ooreenstemming met aangehaalde literatuur. Dit is onwaarskynlik dat seleksie vir Iiggaamsmassa nadelige gekorreleerde reaksies in reproduksie sal veroorsaak, tensy Iiggaamsmassa op 'n baie jong ouderdom as seleksiekriterium gebruik word